Control circuitry for crossbar switches



I Nov. 4, 1969 T, F.'DOUGHERTY, JR; ET AL 8 CONTROL CIRCUIIRY FOR CROSSBAR SWITCHES Fild April 7. 1966 2 Sheets-Sheet 1 FIG.

{OPERATOR POSITION 20 I THOUSANDS 9& Q Q I ST-! 4 HUNDREDS I l START KEY 42 1 L FROM FROM OTHER PREF- OTHER L.O.CGT. 0 OTHER T. F. DOUGHERTY. JR. lNl/ENTORS: W.J. MAC NUTT By W.J MC KELVEY ATTORNEY Nov. 4, 1969 1-. F. DOUGHERTY, JR., E L 3,476,930

CONTROL CIRCUIIRY TOR CROSSBAR SWITCHES Filed April 7. 1966 2 Sheets-Sheet 2 SOURCE vlo NW ND-II II fusT-e' NCS-3 DISPLAY FOR POS. NO- N COMMON YTRANS- LATOR TREE DISPLAY FOR P08. No.20

United States Patent U.S. Cl. 317-157 6 Claims ABSTRACT OF THE DISCLOSURE Crossbar switches connect any one of 10,000 input signals to display equipment as determined by rotary selector switches at operator positions. Rotary switches determine the operation of the desired hold and select magnets of the crossbar switches. A second bank of contacts on each rotary selector switch is series connected in a ground path to a transistor timer and detector circuit. The release of priorly selected crosspoints is effected by opening this ground path. The timer distinguishes between true and false release signals on this path. The ground path is also opened to release selected crosspoints if a double connection is attempted through the crossbar switch.

BACKGROUND OF THE INVENTION This invention relates to circuitry for the control of crossbar switches and more particularly to such circuitry for assuring proper release of the hold magnets of crossbar switches.

Crossbar switches, as is well known, select a particular crosspoint by the selective energization of a select magnet'and a hold magnet, the switch crosspoint being then held locked up by energization of the hold magnet alone. Release of the operated crosspoint thus requires only the de-energization of the hold magnet.

It is important however that the hold magnet be released only when a true release signal has been generated and not be released improperly because of some transient electrical noise or spurious signal.

Accordingly, it is a general object of our invention to enable release of hold magnets in crossbar switches only in response to valid release signals.

More specifically it is an object of our invention to release a hold magnet when a new connection is to be established through the crossbar switch, but nevertheless to keep the hold magnet operated in spite of false signals which ordinarily would cause the hold magnet to release.

It is a still further object of our invention to utilize the same circuitry both to detect release signals and to prevent a hold magnet from locking up if more than one input signal bearing crosspoint common to the hold magnet is operated at the same time.

BRIEF SUMMARY OF THE INVENTION In one specific illustrative embodiment of our invention, a crossbar switch array may be selectively controlled for signal distribution purposes at any of a plurality of operator positions so that a particular operator may have displayed at her position any of a larger number of input signals without disturbing the display of that signal before any other position. More specifically, the particular signal to be displayed is selected by operation of a number of rotary selector switches at the oper'ator position and means are provided to insure against two signals being simultaneously displayed at the same position.

In accordance with out invention, a second bank of contacts of each rotary selection switch is series connectedv in a ground path to a transistor timer and detector circuit. More particularly, this ground path normally applies ground to the base of a first transistor maintaining it,.and an associated relay, unoperated. Operation of any of vthe selector switches to change the selected crosspoints in the crossbar switch initiates the operation of the detector circuit to effect release of the hold magnet by opening this ground path; this release is actually effected by operation of the aforementioned relay in the transistor v,detector circuit, back contacts of this relay being in the locking paths of the hold magnets.

The detector circuit guards against false release signals'by preventing energization of this relay for a predetermined time after opening of the ground path through the banks. of the rotary selector switches. If the interruption of. the ground signal persists beyond this time, a genuine hold magnet release signal is presumed, and the circuit. energizes the relay to restore the hold magnets. Further, in accordance with an aspect of our invention, a double input signal crosspoint connection also causes interruption of this ground path, thereby also initiating detection of the release condition and operation of this relay to release the hold magnets.

The transistor detector circuit, in accordance with our invention, includes a pair of transistors, a break down device, and an RC circuit to perform the timing function to ensure that the release pulse has persisted for the required minimum period. Ground is normally chained through each contact on one of the banks at each of the rotary switches, all wired in series, to back bias a diode connected to the base of one of the transistors, maintaining it normally off. When this ground is removed, as by rotation of one of the selecting switches, this transistor turns on and, after a timed interval, the break down device conducts and causes the other transistor, which is of opposite conductivity type, to turn on.

When the second transistor turns on, its collector current now supplies the base drive for the first transistor and the two transistors are latched in the on state, thereby operating the release relay which interrupts the holding current paths for the hold magnets. Once the second transistor turns on, the detector circuit is set and the control of the detector circuit by the ground path through the selector switches is nullified. The diode in the ground path prevents the reapplication of ground from turning off the transistors. The relay in the collector circuit of the first transistor remains operated until the reapplication of ground through a distinct path separate from the series ground path through the rotary selection switches.

It is a feature of our invention that release of the hold magnets of crossbar switches be controlled by a transistor detector and timer circuit enabled by a ground path series connected through the contacts of the selection switches, which determine the selection of the crosspoints in the crossbar switches.

It is another feature of our invention that the detector circuit include a pair of transistors which are normally off, the interruption of the series ground path biasing a first transistor on, which, in turn, biases the second transistor on after a timed delay, the two transistors then being latched in the on condition so that subsequent reappearance of the ground on the series ground path is ineffective to turn off the detector circuit.

It is a further feature of our invention that a separate ground path be provided for resetting the detector circuit, the separate ground path being distinct from the series path through the selection switches.

It is still another feature of our invention that the series ground path can also be interrupted by circuitry responsive to the attempted double connection of two inputs through the crossbar switches.

These and other objects and features of our invention may be more fully understood from a consideration of the following detailed description together with the accompanying drawing.

DESCRIPTION OF THE DRAWING FIGS. 1 and 2, when placed together side by side, represent a schematic drawing of one illustrative embodiment of our invention.

DETAILED DESCRIPTION Turning now to the drawing, there is depicted one illustrative embodiment of our invention wherein crossbar switches are manually controlled through selector switches and wherein, in accordance with our invention, a control circuit distinguishes between authentic and erroneous signals for releasing the hold magnets of the crossbar switches.

More specifically, as can be seen in the drawing, the system may connect any of a large number of inputs 10, which may be even of the order of 10,000, through crossbar switches 11 to an output device 12- associated with each operator position. The selection of the particular input 10 is determined at an operator position 20, of which a number may be provided in a single system. Specifically, the illustrative operator position 20 has four selecting switches 30, 32, 34, and 36 which each have ten contact positions. These selecting switches control a conventional relay translator tree 15 to energize the individual select magnets Sa Sn in the crossbar switches 11. Inasmuch as the translator tree 15 may be of conventional design, it need not be described in detail herein.

Each of the 10,000 input signals is assigned arbitrarily a number in the group from 0000 to 9999'. To enable an individual input signal to be connected through the crossbar switches to the display device 12-1 associated with the illustrative position 20, the number assigned to that input is set up by the operator on the rotary selecting switches 30, 32, 34, and 36. Because six wire crosspoints are employed in crossbar switch 11 whereas each of signal inputs 10 requires only two wires, each crosspoint of crossbar switch 11 may carry a pair of signal inputs. The setting of selecting switches 30, 32, 34, and 36 operates one of select magnets Sa Sn which, in turn, operates a crosspoint common to two of signal inputs 10. To insure that only one of the two signals available at the aforementioned crosspoint is actually delivered to display device 121 switch 36 is equipped with a second bank of contacts 40. In bank 40 all of the contacts to which odd si nal numbers have been assigned are wired together and similarly all of the contacts to which even numbers have been assigned are wired together. When switch 36 is positioned to designate one digit of a signal number, the wiper blade for bank 40 completes a circuit for select magnet 481 or 482. Each of these select magnets controls a respective steering level crosspoint in switch 11 which selects one or the other of the signals common to the crosspoint selected by the operation of one of select magnets Sa Sn.

In operation, start key contacts 42 at operator position 20 are closed to apply battery 44 to the winding of the start relay ST through preference lockout circuit 13. The other operator positions are provided with a similar path through circuit 13 which prevents more than one ST relay from being operated at a time. Relay ST connects battery 44 through contacts ST-l through ST- to the wiper blades of the selecting switches and thus to the translator tree 15, thereby causing battery to be applied to the designated select magnets S- and 48- of the crossbar switches 11.

Operation of the designated select magnets 4S- and S- completes operating paths through contacts 1W and contacts W by operation of relays 1W and W, not shown but as is known in the art, for operation of the appropriate hold magnets lHM and HM through start relay contacts ST6. Advantageously in this embodiment hold magnet 1HM and one other hold magnet, such as 2HM, are energized on each connection to display 121. Six such additional hold magnets 2HM-7HM may be utilized in this embodiment.

To keep the crosspoints operated, the hold magnets selected are locked up. To insure that one of select magnets Sa Sn has, in fact been operated before allowing the hold magnet to lock, the locking path for the hold magnet includes a make contact of supervisory relay CS and off normal contacts, such as 2HM-1, of the selected hold magnet, such as ZHM. The operating path for relay CS is completed from ground through a resistor, such as resistor 86a, associated with the crosspoint operated by select magnet Sn, and through the winding of marginal check relay CK to the winding of the supervisory relay CS. Relay CS operates its contacts CS-3 in the locking path for the hold magnets.

The operator position 20 is disconnected from the translator tree through the operation of the supervisory relay CS break contacts CS-l which interrupt the holding path for the start relay ST, thereby removing battery from the selector switches 30, 32, 34, and 36. This in turn causes release of the select magnets which had been energized; this interrupts the operating paths for the hold magnets to ground through the contacts of relays W and contacts ST-6.

In accordance with an aspect of our invention, the hold magnets are released through operation of a circuit which distinguishes between valid release signals and invalid or spurious ground pulses. In operation, manipulating any of the rotary selecting switches 30, 32, 34, 36 to move a wiper blade from one contact to another releases the operated hold magnets and restores the crosspoints.

Each of these rotary selecting switches is equipped with contact banks 46, 48, 50, and 52, respectively, and the contacts in each of these banks are connected in series to the wiper blade of the adjacent bank. This arrangement of contacts is connected on one side to ground and on the other side through break contacts CK-l to the junction of resistor 56 and diode 58. This ground shunts down resistance battery 54 and prevents the base of a normally off transistor 26 from being forward biased. Consequently, moving any wiper blade to select another input signal temporarily disconnects this ground, and a negative potential is available to forward bias diode 58 and also the base-emitter junction of transistor 26. Thus, when ground is removed from the base of transistor 26, the transistor is biased on through a path from power supply 54, resistor 55, resistor 56, and diode 58. Transistor 26 then charges capacitor 29 through a circuit from ground, varistors 47 and 49, the emitter-collector path of the transistor '26, resistor 33 and resistor 55fto supply 54. The time required to charge capacitor 29 to the point where it no longer short circuits the winding of relay D determines the delay interval (advantageously of 200 microseconds) for discriminating against spurious pulses which might be caused by contact vibration and the like. When the absence of ground at the junction of resistor 56 and diode 58 permits transistor 26 to remain on long enough to break down Zener diode 35, transistor 28 is turned on. Transistor 28 then provides through its emitter-collector junction a base current path for transistor 26 which will not be interrupted by the reappearance of ground at the junction of resistor 56 and diode 58. Transients, however, will ordinarily last considerably less than the interval chosen, such as 200 microseconds, and, accordingly, a large safety factor is obtained against not detecting a valid open interval.

After Zener diode 35 conducts, transistor .28 is biased into operation through a path from ground, varistors 47 and 49, the emitter-collector path of transistor 26, resistor 33, Zener diode 35 and resistor 37 to the base of the transistor 28, resistor 38, and resistor 55 to supply 54. Transistor 26 now supplies the base current for transistor 28 as well as an operating current for the relay D. Relay D then opens break contact D1, which interrupts the looking path for the hold magnets and restores the crossbar switches to normal.

Transistors 26 and 28 remain activated because the collector electrode of transistor v28 now provides the base current for transistor 26 through resistor 60. The exchange of base currents between transistors 26 and 28 maintain both transistorsin operation to prevent any hold magnet from locking up.

When the transistors 26 and 28 are thus latched in their conducting states, reapplication of ground through the series path including the selector switch banks 46, 48, 50, 52 is prevented from interrupting the transistor operation by the inclusion of the diode 58 in their series path.

The transistor circuit and relay D are de-energized by once more manually operating the start key 42 again to energize relay ST which, by closing its make contacts ST-.7, grounds the base of transistor 26. Turning off transistor 26 also turns 01f transistor 28 and releases relay D, thereby closing the break contacts in the locking paths of the hold magnets. Operation of relay ST also cioses its contacts ST-8 thereby completing an obvious path for operation of slow operate relay E. Relay E in operating in turn opens its normally closed contacts E-l in the ground path for the base of transistor 26'. Accordingly, a reset ground pulse equal to the operate time of relay E, which may 'be of the order of 5 milliseconds, is applied when the start relay is reoperated. As relay E releases after release of the start relay ST, this ground reset path remains open and control of the transistor detection circuitry is returned to the series ground lead through the rotary selection switches. Advantageously, a single relay E may be utilized for all operator positions, the winding being multipled to the individual contacts ST-8 of each position and the contacts E-l being multipled to the individual contact ST-7 of each positon.

When transistor 26 turns ofi, capacitor 29 can then discharge through parallel paths, including a path including Zener diode 35, resistor 37, the base emitter path of still conducting transistor 28 to supply 54 and a path through resistor 33 and relay D. Upon discharge of capacitor 29, diode 35 again becomes nonconducting and transistor 28 turns off. Resistor 38 is of a relatively high resistance with respect to this discharge path.

Advantageously, a diode 53 may be connected across the-winding of relay D to prevent transient spikes due to the inductance of the relay coil from damaging transistor 26, as is known in the art.

Thus in keeping with the principles of our invention, a transistor controlled relay circuit is provided to release the hold magnets when a new connection is being established through the crossbar switch. This relay circuit, however, keeps the hold magnets operated in the presence of spurious ground pulses which would ordinarily cause the hold magnets to release.

In accordance with another aspect of our invention, this same circuitry is utilized if marginal check relay CK detcts more than one input signal simultaneously connected by operated crosspoints to the display equipment. The check magnet CK is connected in series with a vertical in the crosspoint switches, to which vertical are connected resistors, such as resistors 86a-86g. These resistors are such that normally the check relay cannot draw sufiicient current to operate. However, if multiple connections are made, parallel resistor paths to ground are provided through the check relay, causing that relay to operate. Relay CK then operates its break contacts CK1 in the selecting switch grounding circuit of transistor 26. If this break in the ground circuit continuity lasts longer than the predetermined minimum time period of the transistor circuitry, then relay D will operate in the manner previously described to release the hold magnets.

Hold magnets HM and associated relays -CK and -CS are provided for each operator position in the system and cooperate with a unique vertical file of crosspoints in the crossbar switch array 11. Similarly each operator position includes a detector circuit and relay D whose contacts, such as ND1, are included in the hold paths of the hold magnets, such as NHM.

It is to be understood that the above described arrangements are merely illustrative of the principles of our invention and that various other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1."A crossbar switching system comprising crossbar switch means having a plurality of select and hold magnets, means including selector switch means for energizing said" select and hold magnets for selectively closing said crossbar switch means, and means for releasing said hold m agriets on reoperation of said selector switch means, said releasing means including a s'eriesground path including series connected contacts of said selector switch means, said ground path being "interrupted on reoperation of said selector switch means, and detector circuit means connected to said series ground path for timing the interruption of said ground path.

2. A crossbar switching system in accordance with claim 1 wherein said detector circuit means includes a first normally off transistor to the base of which said series ground path is connected and a second normally off transistor of opposite conductivity type whose base is connected in the collector circuit of said first transistor and whose collector is connected to the base of said first transistor.

3. A crossbar switching system in accordance with claim 2 further comprising timer means cnergizable by said first transistor for delaying operation of said second transistor and relay means in the collector circuit of said first transistor, said relay means including normally closed contacts in the holding current path of said hold magnet.

4. A crossbar switching system in accordance with claim 3 wherein said timer means includes a resistor and capaictor connected in parallel of said relay means and further including a breakdown diode connected between said capacitor and said second transistor base in the connection between said second transistor base and said first transistor collector.

5. A crossbar switching system in accordance with claim 1 further comprising diode means in said series ground path for preventing reappearance of ground on said ground path from disabling said detector circuit means and a further reset ground path connected to said detector circuit means for resetting said detector circuit means.

6. A crossbar switching system in accordance with claim 1 further comprising means for detecting double operation of said crossbar switch means, means responsive to said double operation detecting means for interrupting said series ground path, and means responsive to operation of said detector circuit means for interrupting the holding current paths for said hold magnets.

References Cited UNITED STATES PATENTS 3,153,176 10/1964 Clay 317-157 WILLIAM C. COOPER, Primary Examiner US. Cl. X.R. 179-22, 27 

